This invention relates in general to vapor compression heating and refrigerating systems. In particular the invention relates to heat pumps and refrigerating machines for respectively heating or cooling a volume.
A major element of lost work in vapor compression machines such as heat pumps and air conditioners is the loss due to throttling the condenser liquid to the evaporator. The Coefficient of Performance (COPH) of such a system is in accordance with the equation: EQU COPH=(h.sub.b =h.sub.e)/(h.sub.c -h.sub.b)
where
h.sub.c =enthalpy of superheated vapor after compression and PA1 h.sub.b =enthalpy of vapor after heated in evaporator and entering the compressor and PA1 h.sub.e =enthalpy of condensed liquid after cooling in condenser
From the formula it is seen that the COPH is increased for either a warming or cooling machine by extracting heat from the condensed liquid. Where subcooling of post-condenser liquid is accomplished without affecting compression work then there is a gain in useful heating or cooling effect with a resulting increase in COPH and Capacity.
The described low temperature heating acquisition is even more beneficial to COPH than would be the effect of reversably expanding the liquid and applying the expansion work to reduce the net compression work. An example would be a heat pump evaporating at 5.degree. F. and condensing at 100.degree. F. with a compression efficiency of 55% and condenser subcooled to 85.degree. F. resulting in a COPH of about 3.2. A reversible liquid expander from 85.degree. F. to 15.degree. F. would return about 5% of the compression gross work and increase the COPH to about 3.45, while subcooling from 85.degree. F. to 15.degree. F. usefully would increase the Capacity about 19.4% and raise the COPH to about 3.85. A problem which exists in applying these concepts to heat pump systems is that of providing a useful heating load of below 70.degree. F.
In houses and other building structures a major component of heat loss amounting to about 20% to 40% comprises infiltration of the heating load from ambient. This results when the inside air of about 70.degree. F. is replaced with cold ambient air which leaks into the structure as the air is driven by stack effect and wind.